Mass estimation method and x-ray inspection apparatus

Abstract

A mass estimation method includes a step of generating X-ray transmission image data for each transmission region of a sample of an inspection object, a step of generating a histogram of pixel values of pixels that are included in N pieces of the X-ray transmission image data of the sample and that correspond to the respective transmission regions, a step of generating a histogram matrix consisting of N row vectors corresponding to N histograms of the sample, a step of using a product of the histogram matrix and a weight vector consisting of a weight coefficient for each pixel value of the N pieces of X-ray transmission image data, to calculate the weight vector that minimizes a variance of the N relative mass estimation values, and a step of estimating mass of the inspection object by using the weight vector.

What is claimed is: 
     
         1 . A mass estimation method comprising:
 a first transport step of transporting a sample that is the same type as an inspection object and that has known mass N times while irradiating the sample with X-rays;   a first X-ray transmission image data generation step of generating, for each transportation, X-ray transmission image data corresponding to a transmission amount of the X-rays for each transmission region of the sample transported in the first transport step;   a first histogram generation step of generating a histogram of pixel values of pixels that are included in N pieces of the X-ray transmission image data of the sample generated in the first X-ray transmission image data generation step and that correspond to the respective transmission regions;   a histogram matrix generation step of generating a histogram matrix consisting of N row vectors corresponding to N histograms of the sample generated in the first histogram generation step;   a weight vector calculation step of using a product of the histogram matrix and a weight vector consisting of a weight coefficient for each pixel value of the N pieces of X-ray transmission image data as a relative mass estimation value vector consisting of N relative mass estimation values of the sample, to calculate the weight vector that minimizes a variance of the N relative mass estimation values; and   a mass estimation step of estimating mass of the inspection object that is transported, by using the weight vector calculated in the weight vector calculation step.   
     
     
         2 . The mass estimation method according to  claim 1 , further comprising:
 a relative mass estimation value vector calculation step of calculating the product of the histogram matrix and the weight vector calculated in the weight vector calculation step as the relative mass estimation value vector; and   a reference mass calculation step of calculating a representative value of the N relative mass estimation values included in the relative mass estimation value vector calculated in the relative mass estimation value vector calculation step as reference mass.   
     
     
         3 . The mass estimation method according to  claim 2 , further comprising:
 a second transport step of sequentially transporting one or more inspection objects that are transported, while irradiating the one or more inspection objects with X-rays;   a second X-ray transmission image data generation step of generating X-ray transmission image data corresponding to a transmission amount of the X-rays for each transmission region of the inspection object transported in the second transport step; and   a second histogram generation step of generating a histogram of pixel values of pixels that are included in the X-ray transmission image data of the inspection object generated in the second X-ray transmission image data generation step and that correspond to the respective transmission regions,   wherein the mass estimation step includes
 a histogram vector generation step of generating a histogram vector consisting of one row vector corresponding to the histogram of the inspection object generated in the second histogram generation step, 
 a relative mass calculation step of calculating a product of the histogram vector and the weight vector calculated in the weight vector calculation step as relative mass of the inspection object, and 
 a mass conversion step of converting the relative mass into the mass of the inspection object based on a ratio between the known mass of the sample and the reference mass. 
   
     
     
         4 . The mass estimation method according to  claim 3 , further comprising:
 a mass pass/fail determination step of determining whether the mass converted in the mass conversion step is within a predetermined mass tolerance corresponding to the inspection object.   
     
     
         5 . An X-ray inspection apparatus comprising:
 a transport unit that transports a sample that is the same type as an inspection object and that has known mass N times;   an X-ray source that irradiates the sample transported by the transport unit with X-rays;   an X-ray detector that detects the X-rays transmitted through the sample for each transmission region of the sample;   an X-ray transmission image data generation unit that generates, for each transportation, X-ray transmission image data corresponding to a transmission amount of the X-rays for each transmission region of the sample based on detection information of the X-ray detector;   a histogram generation unit that generates a histogram of pixel values of pixels that are included in N pieces of the X-ray transmission image data of the sample generated by the X-ray transmission image data generation unit and that correspond to the respective transmission regions;   a histogram matrix generation unit that generates a histogram matrix consisting of N row vectors corresponding to N histograms of the sample generated by the histogram generation unit;   a weight vector calculation unit that uses a product of the histogram matrix and a weight vector consisting of a weight coefficient for each pixel value of the N pieces of X-ray transmission image data as a relative mass estimation value vector consisting of N relative mass estimation values of the sample, to calculate the weight vector that minimizes a variance of the N relative mass estimation values; and   a mass estimation unit that estimates mass of one or more inspection objects transported by the transport unit, by using the weight vector calculated by the weight vector calculation unit.   
     
     
         6 . The X-ray inspection apparatus according to  claim 5 , further comprising:
 a relative mass estimation value vector calculation unit that calculates the product of the histogram matrix and the weight vector calculated by the weight vector calculation unit as the relative mass estimation value vector; and   a reference mass calculation unit that calculates a representative value of the N relative mass estimation values included in the relative mass estimation value vector calculated by the relative mass estimation value vector calculation unit as reference mass.   
     
     
         7 . The X-ray inspection apparatus according to  claim 6 ,
 wherein, in an inspection mode in which the one or more inspection objects are transported by the transport unit,
 the X-ray source irradiates the inspection object that is transported by the transport unit with X-rays, the X-ray detector detects the X-rays transmitted through the inspection object for each transmission region of the inspection object, 
 the X-ray transmission image data generation unit generates the X-ray transmission image data corresponding to a transmission amount of the X-rays for each transmission region of the inspection object based on detection information of the X-ray detector, and 
 the histogram generation unit generates a histogram of pixel values of pixels that are included in the X-ray transmission image data of the inspection object generated by the X-ray transmission image data generation unit and that correspond to the respective transmission regions, and 
   the mass estimation unit includes
 a histogram vector generation unit that generates a histogram vector consisting of one row vector corresponding to the histogram of the inspection object generated by the histogram generation unit, 
 a relative mass calculation unit that calculates a product of the histogram vector and the weight vector calculated by the weight vector calculation unit as relative mass of the inspection object, and 
 a mass conversion unit that converts the relative mass into the mass of the inspection object based on a ratio between the known mass of the sample and the reference mass. 
   
     
     
         8 . The X-ray inspection apparatus according to  claim 5 , further comprising:
 a foreign matter determination unit that determines whether a foreign matter is contained in the inspection object based on the detection information of the X-ray detector.   
     
     
         9 . The X-ray inspection apparatus according to  claim 6 , further comprising:
 a foreign matter determination unit that determines whether a foreign matter is contained in the inspection object based on the detection information of the X-ray detector.   
     
     
         10 . The X-ray inspection apparatus according to  claim 7 , further comprising:
 a foreign matter determination unit that determines whether a foreign matter is contained in the inspection object based on the detection information of the X-ray detector.